Abstract
Wool and hair fibres consist of a variety of proteins, including the keratin-associated proteins (KAPs). In this study, a putative ovine homologue of the human KAP21-2 gene (KRTAP21-2) was identified. It was located on chromosome 1 as a 201-bp open reading frame (ORF) in the ovine genome assembly from a Texel sheep (v.4 NC_019458.2: nt122932727 to 122932927). A polymerase chain reaction- single strand conformation polymorphism (PCR-SSCP) analysis of this ORF, and subsequent DNA sequencing, identified five sequences (named A-E). The putative amino acid sequences that would be produced, shared some identity with each other and with other KAPs, but they were most similar to ovine KAP21-1, and phylogenetically related to human KAP21-2. The location of the ovine KRTAP21-2 sequence was consistent with the location of human KRTAP21-2, and this suggests they represent different variant forms of ovine KRTAP21-2. Variation in this gene was investigated in 389 Merino (sire) × Southdown-cross (ewe) lambs. These were derived from four independent sire-lines. The sequence variation was found to be associated with variation in five wool traits: including mean staple length (MSL), mean fibre diameter (MFD), fibre diameter standard deviation (FDSD), prickle factor (PF), and greasy fleece weight (GFW). The most persistent effect of KRTAP21-2 variation was with variation in MSL; with the MSL of sheep of genotype AC being 12.5% greater than those of genotype CE. A similar effect was observed from individual variant absence/presence models. This suggests that KRTAP21-2 should be further investigated as a possible gene-marker for improving MSL.
Highlights
Wool is a complex structure composed of numerous proteins
We describe the characterization of this open reading frame (ORF), report sequence variation in it that was detected by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis and DNA sequencing, and reveal associations between this gene variation and variation in some important wool fibre traits
The PCR primers were designed to amplify the ORF and upon sequencing the amplicons were confirmed to be of 294 bp in size
Summary
The large and diverse family of keratin-associated proteins (KAPs) fulfil an important structural role, as they are components of the matrix in which the keratin intermediate filaments (KIFs) are embedded. They are believed to play an important role in defining the physical and mechanical properties of wool fibres [1]. Of these KAPs, HGT-KAPs are predominantly found in the wool fibre orthocortex, and they have been revealed to be the first KAPs expressed after the synthesis of the KIFs. The proportion of the wool fibre that is HGT-KAP varies in different wools, varying up to 12% by weight in the wool of Merino sheep, to less than 1% by weight in wool from Lincoln sheep [3]. The small amount of HGT-KAP in sheep with the felting lustre mutation and the wide range of content of HGT-KAP in wool from different sheep breeds [4], suggests these proteins have a novel role in determining wool fibre characteristics
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